Many situations in industry, for example in chemical industries, nuclear power industries, and oil and gas industries including downhole and subsea applications, require measurement of a flow rate of a fluid through a conduit, for example through a pipe. Moreover, when a temperature measurement and a pressure measurement across an orifice, through which the fluid flows, are made, it is feasible to infer a density and a viscosity of the fluid, for example via performing computations. However, an issue of measurement accuracy arises when the fluid flow is turbulent and/or is spatially inhomogeneous. Situations of spatial non-homogeneity arise, for example in petrochemicals industries wherein fluids pumped from an oil well often include a mixture of oil, water, gas and sand particles. Moreover, physical characteristics of such a flow are susceptible to changing considerably on an onset of turbulent flow. Many known reported flow measuring apparatus are designed to cope with non-turbulent flows, and will potentially generate erroneous flow measurements when confronted with complex flows, for example turbulent flows. There is a contemporary need for highly accurate non-invasive flow measuring apparatus for monitoring flows of crude oil containing fractions of water and/or gas.
In a published European patent document EP 2 431 716A1 (“A multiphase flow meter and a correction method for such a multiphase flow meter”, Applicant—Services Petroliers Schlumberger, Paris, France; inventors—Lupeau & Baker), there is described a flow meter for measuring a flow rate of a multiphase fluids mixture comprising at least one gas phase and one liquid phase, wherein the flow meter comprises:    (i) a pipe section through which the multiphase fluid mixture flows comprising a throat between an upstream part and a downstream part such as to generate a pressure drop between the upstream part and the downstream part; and    (ii) a fraction measuring device for estimating a fractional flow rate for each phase of the multiphase fluid mixture passing through the throat.
The flow meter further comprises at least one ultrasonic sensor which is operable to estimate a thickness of the liquid phase flowing as a liquid film along the wall of the pipe section, wherein the thickness is used to correct the estimated fractional flow rate for each phase when a gas liquid fraction (GLF) pertaining to the multiphase fluid mixture is such that the gas phase flows in a core of the pipe section, and the liquid phase flows along the wall of the pipe as the liquid film.
Referring to FIG. 1, an off-shore environment is indicated generally by 10, wherein a sea-bed assembly 30 is submerged in water 20, and is coupled via one or more sea-bed pipelines 40 to a petrochemicals processing facility 50. The assembly 30 is alternatively, or additionally, coupled via the one or more pipelines 40 to a floating oil platform (not shown). The sea-bed assembly 30 is coupled via a bore hole 60, for example defined by a liner tube, to a subterranean anticline including oil and/or gas resources. In many situations, the sea-bed assembly 30 is more than 1 km deep in the water 20 and is potentially subject to a pressure of 150 Bar or more. It is desirable to measure to a high accuracy a flow rate of a complex fluid being drawn up through the bore hole 60, for example. However, an environment experienced by the sea-bed assembly 30 is challenging for any type of precision flow meter. Although flow through the bore hole 60 may, for example, often be substantially non-turbulent, potential situations can be arise where highly turbulent flow rates can occur, for example in a event of a leak or unexpected pressure surge from the anticline, wherein it is highly desirable to be able to measure flow rates of complex fluids, even under turbulent conditions. Known types of flow meter are not able to provide such measurement flexibility and yet be able to withstand, over a long period of use, harsh environmental conditions associated with operation of the sea-bed assembly 30.
In a published US patent document US2008/163700A1 (Huang Songming), there is described a measuring apparatus for measuring properties of a flow of a fluid within a conduit including one or more walls, wherein the apparatus includes a transducer arrangement including transducers for emitting and receiving ultrasonic radiation in upstream and downstream directions in respect of the flow of fluid, and a signal processing arrangement for generating signals to excite the transducer arrangement and for processing received signals provided by the transducer arrangement for generating output signals from the signal processing arrangement indicative of properties of the flow. Moreover, there is also disclosed for the upstream and downstream directions that the apparatus is operable to perform measurements along first and second paths associated with each of the directions; for the first path, the transducer arrangement in cooperation with the conduit is operable to provide the first path solely via the one or more walls for Lamb-wave ultrasonic radiation coupling directly from a transducer for emitting ultrasonic radiation to a transducer for receiving ultrasonic radiation to generate a first received signal. Furthermore, for the second path, the transducer arrangement in cooperation with the conduit is operable to provide the second path for propagation of ultrasonic radiation within the one or more walls via Lamb waves coupling to at least a portion of the flow to propagate through the flow from a transducer for emitting ultrasonic radiation to a transducer for receiving ultrasonic radiation to generate a second received signal. The signal processing arrangement is operable to determine from the first and second signals ultrasonic radiation propagation time period through the first path and through the second path in each of the upstream and downstream flow directions, and to perform computational operations in respect of at least one of: a flow velocity (v) of the fluid in the conduit, a velocity of sound (c) through the fluid. Another published United States patent application US2008/163692A1 (Huang Songming) also describes a generally similar type of apparatus to that described in the aforesaid US patent application US2008/163700A1.
In a United Kingdom patent document GB2 399 412A (“Multiple phase fraction meter having compliant mandrel deployed within fluid conduit”, Applicant—Weatherford/Lamb Inc.), there is described a hollow mandrel which is deployable within a production pipeline at least partly within a length of a speed-of-sound or phase-fraction meter. Sensors of the meter comprise Bragg gratings and wraps of fibre optic cable whose lengths are sensitive to acoustic pressure disturbances in the pipeline. A passive fibre optic based flow velocity meter is thereby provided, and the mandrel is optionally shaped to form an annular venture meter to provide an alternative implementation for calculating the fluid mixture density for purposes of double checking or calibration.
In a published PCT patent document WO 2008/073673A1 (“Ultrasonic Flow Rate Measurement using Doppler Frequency”, Applicant—General Electric Company), there is described a method of determining a flow rate of a fluid in a conduit. Ultrasonic energy is directed through the conduit along multiple paths. The ultrasonic energy is detected and measured using a range-gated Doppler technique to determine the velocity of the fluid at several points in the conduit. The point velocities are used to calculate the average flow rate of the fluid in the conduit.
In a published U.S. Pat. No. 6,047,602 (“Ultrasonic buffer/waveguide”, Applicant—Panametrics Inc.), there is described a waveguide for coupling ultrasonic energy from a source on one side of a fluid-bounding wall, such as a conduit, into fluid on the other side of the wall. The waveguide has a buffer that couples to the source, and a seat with an exit face, and an intermediate portion includes a redirecting surface for internally redirecting energy propagated along the buffer towards the exit face to exit as a narrow directed beam. The waveguide core has a rectangular cross-section which is narrow, namely has an aspect ratio above two, and the buffer has a length which is effective to isolate thermally and to protect the source from the conduit. The waveguide is attached via clamp-on or welding to a pipe or spool-face. Optionally, the buffer is a thin tube which couples shear waves into the seat portion, which has a rectangular cross-section.
In a published United States patent document U.S. Pat. No. 7,185,547B2 (“Extreme temperature clamp-on flow meter transducer”, Applicant—Siemens Energy and Automation Inc.), there is described a device for measuring flow in a pipe. The device includes a first metal plate mounted to the pipe. The first metal plate includes a first contact portion for contacting a wall of the pipe and a first away portion spaced apart from the wall of the pipe. The device further includes a second plate including a second contact portion spaced apart from the wall of the pipe. A first transducer is mounted to the first away portion. Moreover, a second transducer is mounted to the second away portion. The first and second transducers are thereby mounted spatially remotely from the wall of the pipe.
In a published U.S. Pat. No. 8,090,131 B2 (“Steerable acoustic waveguide”, Applicant—Elster NV/SA), there is described a steerable acoustic waveguide apparatus which includes a plurality of plates arranged in one or more linear arrays. Steering of an acoustic beam radiated from the waveguide apparatus may be achieved through differential delays of acoustic signals resulting from differences in timing, frequency, or mode or resulting from difference in physical attributes of the plates. The waveguide apparatus serves as a thermal buffer, and may simplify access to an acoustic path in a device such as an ultrasonic flow meter.